Multi-core audio optimizations for Mac M1/2 CPUs

[taktik]

Unfortunately, there is no simple switch/way to do this. This old quote from Multicore Faq still is true:

@taktik

2 CPUs = 2x performance speedup?

Unfortunately its not that easy. Handling multiple CPUs first costs the engine a bit of performance (you need to take care of the multiple “audio streams”), but this is in overall not very much. The amount of this overhead is visible when enabling/disabling the multicore support in an empty song (not playing back anything).
Then Renoise has to split your song int “independent streams” that the CPUs can then handle separately. In complex songs with a lot of send tracks and devices this limits the sharing capabilities a bit, which means that the performance is not very well balanced.

If you have 10 VSTs running and nine of them use almost no CPU power, but one uses most of it, Renoise can’t magically make the heavy VST faster. Only the VST itself could do that.

Also, to create “independent streams” you can’t split tracks that feed into each other (-> groups/sends), so some tracks have to be computed on a CPU to keep the signal path connected.

I’m sure there will be further optimisations here and there, but we need concrete examples and ideas (songs/setups where the current CPU handling seems to be bad). Then we could see what’s going on here and how we can improve things.